The present invention relates generally to active analog signal processing circuits. More particularly, the present invention relates to an active analog signal processing circuit that processes signals associated with multiple channels.
Multiple channel signal processing circuits are common in such applications as cellular telephone systems, stereo audio systems, and home theater systems. For example, the analog front end portion of a cellular telephone system may utilize well known quadrature modulation techniques to process in-phase and quadrature-phase baseband signals associated with different channels (I/Q signals). Conventional multiple channel systems have employed duplicate analog circuits for each signal channel. Such analog circuits typically include a plurality of active circuit components and any number of passive electronic components.
FIG. 1 is a general block diagram representation of a prior art multiple channel processing circuit 100 configured to accommodate an in-phase (xe2x80x9cIxe2x80x9d) input signal 102 and a quadrature (xe2x80x9cQxe2x80x9d) input signal 104. For purposes of this general introduction, the specific function of circuit 100 need not be described in detail; circuit 100 may be utilized in any number of applications such as a switched-capacitor filter, an analog to digital converter, a switched-capacitor digital to analog converter, or the like. In the present context, circuit 100 utilizes discrete time sampling of analog input signals. I-input signal 102 and Q-input signal 104 are each sampled in accordance with a given sampling rate and sampling period. An analog processing circuit 106 associated with the I-input signal 102 includes a number of active circuit components 108 and a number of passive circuit components 110. Similarly, an analog processing circuit 112 associated with the Q-input signal 104 includes a number of active circuit components 114 and a number of passive circuit components 116. Analog processing circuit 106 and analog processing circuit 112 may be substantially identical to one another. In this manner, prior art techniques simply duplicate the analog processing circuits N times to accommodate N signal processing channels.
Analog processing circuit 106 produces an I-output signal 118, while analog processing circuit 112 produces a Q-output signal 120. Output signals 118 and 120 are generated in a sampled manner in response to the particular characteristics of analog processing circuits 106 and 112. Output signals 118 and 120 may be further processed in accordance with any number of conventional techniques depending upon the specific application.
Although the prior art approach may simplify the design aspect of a multiple channel system, it has some practical limitations. For example, as the number of channels increase, the required prior art circuitry will proportionately increase, with a corresponding increase in power consumption and semiconductor die size. However, with the increasing demand for hardware miniaturization, the amount of power, physical size, and number of components associated with semiconductor implementations can place limitations on the design of the analog circuitry. Accordingly, due to practical size and power constraints, the simple duplication of active signal processing circuits may not be a desirable implementation for a multiple channel signal processing application.
A multiple channel signal processing solution in accordance with the present invention utilizes a shared active circuit component to process a plurality of input signals during a sampling period. Rather than merely duplicating an active processing circuit for each input channel, the exemplary system employs at least one common active electronic component in conjunction with similar passive component networks associated with each channel. The reduction of active circuit components results in a reduction of operating power and a reduction in the size of the semiconductor implementation. Thus, a practical embodiment may be realized in a compact manner and without a considerable increase in the power requirements.
The above and other features of the present invention may be carried out in one form by a multiple channel signal processing circuit having a first input associated with a first signal for a first channel, a second input associated with a second signal for a second channel, a network of passive electronic components configured to process samples of the first signal and samples of the second signal, a shared active electronic component configured to process samples of the first signal and samples of the second signal, and a channel switching mechanism configured to switch between processing states associated with the first channel and the second channel during a sampling period.